1. Field of the Invention
This invention relates to a heat shield for clutches and flywheels and, in particular, to a heat shield installation which is universally adaptable for clutches and flywheels of widely varied diameters.
2. Brief Statement of the Prior Art
In most automative and truck vehicles, torque is transmitted to the drive shaft through a clutch disc that is mounted on the drive shaft and received between a pressure plate of the clutch and the flywheel. Resilient springs, either coil springs or a Bellville spring, apply a resilient force to the pressure plate to bias it towards the flywheel, frictionally securing the clutch disc between the pressure plate and the flywheel, and a lever mechanism is provided to release the spring force and retract the pressure plate to disengage the clutch.
Efforts have been made to shield the flywheel and clutch parts against the heat which is generated during operation of the clutch, particularly in racing applications with high engine speeds. Thermally insulating washers have been mounted beneath the clutch springs, and heat shields of various designs have been applied to flywheels. Examples of such heat shields are: steel discs with sintered bronze coatings which are riveted to a flywheel; and coatings of steel or bronze deposited on the face of a flywheel by plasma spraying. These applications are commonly used with aluminum pressure plates and flywheels, since aluminum provides a very poor frictional surface and must be coated with bronze or steel. In most applications, the sintered coating is ground to minimal thickness, usually about 0.080 inch, or less.
While the various prior art approaches have generally been identified as "heat shields", the applications have predominantly been directed to improving the frictional surface in contact with the clutch disc facings, rather than providing optimum heat shielding capability. As an example, very little attention has been directed to isolating the heat and to providing a substantial heat sink on the frictional surface of the flywheel or pressure plate.
Pucks, in the form of ceramic coated copper plates having trapezoidal, or circular segmental shapes have been riveted onto the tips of three- and four-point discs to provide the heat resistance of metallic discs and the lightness of organic discs. Similar pucks have been sintered onto steel discs to provide metallic friction facings in attempts to withstand high temperatures developed by the heat generated in the clutch. Sintered iron facings have been required in slider clutches since the large amounts of heat generated with this competition clutchb would disentegrate a clutch disc with a organic facing. These approaches have unnecessarily compromised the design of the clutch discs, which should have minimal mass and maximum frictional characteristics.
One major difficulty in providing economic retrofitting of a heat shield to clutch pressure plates, or rings, and flywheels has been that these members have a wide variety of diameters and surface areas. The conventional approach of riveting a bronze coated steel disc to the face of a pressure plate or flywheel would thus require that a multitude of heat shields of different diameters be manufactured and stocked in inventory of a parts supply house. Very considerable investments ibn tooling and inventory are thus reqired with the conventional approach. Additionally, considerable care must be exercised in selecting a rivet pattern in a flywheel or pressure plate to avoid structurally weakening the member to such a degree that it will fail when subjected to high rotational speeds.